Behavioral thermoregulation and survival of released Brook Trout following assisted recovery after angling
Ryan Y Hodgson, Luc LaRochelle, Bradley E Howell, Myra Thapar, Peter Holder, Liane Nowell, Jacob W Brownscombe, Steven J CookeAbstract
Objective
Temperature plays a critical role in postrelease outcomes and survival from catch-and-release recreational angling. During warm periods in lentic systems, the ability of coldwater fish such as Brook Trout Salvelinus fontinalis to avoid warm surface waters or other water column regions that exceed thermal thresholds is essential for postrelease recovery. Assisted recovery techniques may aid Brook Trout in navigating to thermally optimal temperatures that facilitate recovery. Our objective was to assess the thermoregulatory behavior of Brook Trout following a novel assisted recovery method.
Methods
We tested the influence of short-term (5 min) holding for recovery at three water temperatures (15, 18, 21°C) on the postrelease temperature and depth use of Brook Trout compared with both immediate release and free-swimming controls. Following capture, we externally attached depth- and temperature-sensing acoustic telemetry transmitters and released fish into open-mesh limnocorrals (2.5 × 10 m depth, 49,000 L) for 72 h to assess their body temperature and depth use across assisted recovery holding treatments. We applied a generalized additive mixed model and post hoc pairwise comparison using simultaneous confidence intervals to examine the impacts of holding temperature, handling time, and body size on postrelease temperature and depth usage.
Results
Our results revealed no significant differences in temperature usage postrelease between our recovery and control treatments. However, we found that longer handling times were associated with warmer water usage postrelease and observed a small number of mortalities (n = 6 of 52) concentrated in our immediate-release and 21°C treatment groups. In general, our findings revealed that postrelease, Brook Trout navigated to 16.2 ± 2.6°C waters relatively quickly (within the first hour) and over time slowly moved into colder water at 12.8 ± 1.9°C.
Conclusions
Overall, our study found minimal differences in thermal behavior of Brook Trout among our temperature recovery holding treatments. However, we did find evidence of a behavioral thermoregulatory strategy in which Brook Trout use warmer water on the upper end of their thermal optima initially and move to colder waters over time. Of relevance for anglers, we found that increased handling time led to higher temperature usage postrelease. Our findings thus indicate that Brook Trout handling should be minimized and immediate release prioritized. We find a lack of evidence for the efficacy of our novel assisted recovery method on Brook Trout in lentic systems during peak summer water temperatures (24.8 ± 1.7°C). Our work contributes to the growing body of literature on catch-and-release assisted recovery tools.